In a typical prior art magnetic disk recording system a slider containing magnetic transducers for reading and writing magnetic transitions flies above the disk while it is being rotated by a spindle motor. The disk includes a plurality of thin films and at least one ferromagnetic thin film in which the recording (write) head records the magnetic transitions in which information is encoded. The magnetic domains in the media on can be written longitudinally or perpendicularly. The shape and size of the pole piece tips at the ABS and any shields are the primary factors in determining the track width. The read and write elements of the head (also called a slider) are built-up in layers on a wafer using thin film processing techniques to form a large number of heads at the same time. FIG. 1 illustrates the prior art relationships between the P2 pole piece tip P2T and the P1 before P1 is milled using P2T as a mask. The section taken is perpendicular to the wafer surface. Only one set of head structures is shown. The thin film for P1 is deposited first followed by the thin film for the gap layer.
FIG. 2 is an illustration of the shape of P1 after ion-milling. The surface of P1 has been milled to form a tip under the gap. The surface of P1 slopes away from the tip. The distance from interface of the gap and P1 to the recessed beveled surface is called the “notch depth”. The process of creating the P1 tip is also called notching. The width of the P1 tip at the gap is called the P1A width. The width of the P2 tip at the gap is called the P2B width. The P1A and P2B dimensions of write pole pieces within the head are critical parameters to the areal density of recording head structures. The view shown in FIGS. 1 and 2 shows the write gap. The track width view (not shown) is perpendicular to the write gap view.
Multiple Ion Mill process steps are used to perform track width trim and P1 notching to control the unique multidimensional structure of the write pole tips. The ion-milling process uses a high voltage source to ionize low pressure gasses, accelerating and neutralizing them through an acceleration grid, creating a nearly neutral beam of atoms which bombards a wafer within the chamber removing material by kinetic or chemical processes. The trimming of track width of pole P2B is achieved by 60°/70° degree ion milling and the P1 notch is defined by 35° to 45° notching of P1 using P2T as a mask. P2B, P1A, (P1A-P2B) and P1 Notch Depth are the critical dimensions of the write pole (P1 and P2) structure. It is very challenging to control all these critical dimensions and achieve a specific design specification. In order to improve critical dimensions control, advanced process control (APC) has been implemented for ion-milling processes. The prior art process control uses feed forward and feedback information to control individual ion-milling steps. Traditional process control methods assume the steps are independent from each other.
Conventionally after the basic structures for the heads have been formed the individual heads rows of heads) are cut from the wafer to expose what will become the air-bearing surface after further processing. The processing of the air-bearing surface typically includes lapping and formation of air-bearing features typically called rails.
FIG. 3 is a block diagram showing selected hardware used in a prior art plating and ion-milling process. The metals used for the pole pieces are deposited by plating. Various precision measurement equipment are used to make measurements at selected stages of the process. Examples include commercially available photolithography measurement tools such as a scanning electron microscope (CD-SEM) made by KLA-Tencor and generic Focused-Ion Beam tools. The measurements are typically made at selected sample sites on the wafer, rather than attempting to measure all of individual heads. The process is automated by connecting the measurement tools and the process equipment to one or more computers which can include a server which integrates data and control over a wide range of process stages and a personal computer which is dedicated to the pole piece tip processing.
FIG. 4 is a flowchart illustrating a prior art process for fabricating the P2T and notching P1. The seed layer for P2 is deposited first 40. A standard photolithography mask is applied and patterned on the wafer for P2 41. The width of P2, which is a critical dimension of the mask, is measured using commercially available tools 42. The metal for P2 is deposited by a plating process 43. The critical dimensions of the P2T are measured 44. A first ion-milling sweep or full rotation milling is performed to remove the seed layer for P2 45. Further ion-milling performs the rough trimming of P2 46. The critical dimensions of the P2T are measured 47 using a FIB tool. An ion-milling sweep or full rotation milling is performed to rough trim 48 and to notch P1 49. The critical dimensions are measured again 50 using a tungsten FIB tool. An ion-milling sweep or full rotation milling is performed to fine trim the P2B 51. The final dimensions of P2T are measured 52. The process proceeds with the deposition of the D2 seed layer 53 which is the copper seed layer for an additional coil layer that is formed in the next phase of the process. The final dimensions of P2B are measured 54 using a FIB tool.
The dotted lines in FIG. 4 represent information flow in the form of feedback and forward. The information gathered in the step of measured P2T 44 is fed forward 61 for use in the ion-milling for notching P1 49. The FIB measurement 47 is fed forward 62 to second ion-milling step to rough trim P2 48. The ion-milling for notching P1 49 also receives feed-back information from 63 from the final P2T measurement 52. The measurement at step 50 is fed forward 64 to fine trimming step for P2B 51. The final P2B measurement 54 is fed back 65 to fine trimming step for P2B 51 as well, but typically by manual adjustment.
Selected prior art steps have been omitted from FIG. 4 to simplify the illustration. The P2 photoresist mask is stripped after P2 is plated. A resist to protect features during subsequent milling is patterned after the first P2B measurement step 47. The protective resist is stripped after last fine trimming step 51. There are other processing steps related to the D2 seed deposition 53 which are unrelated to the subject of the application.
In published U.S. patent application 2003/0223150 by Edward Lee a method of protecting the front P2 pole tip during the ion mill patterning of the yoke is described. A front connecting pedestal is electroplated over the front P2 pole tip slightly behind the ABS, and a back gap connecting pedestal is electroplated over the back gap P2 pedestal. Insulator materials are formed over the front P2 pole tip, over the front connecting pedestal, and in between the front and the back gap connecting pedestals. Next, a chemical-mechanical polishing (CMP) is performed over the top of the structure to form a substantially planar top surface. A full-film of yoke layer materials is then sputter deposited over this top surface, followed by the formation of a photoresist mask slightly behind the ABS. When the yoke layer materials are subsequently ion milled to form the yoke, the front P2 pole tip is protected by the surrounding insulator. The front and back gap connecting pedestals form an intervening magnetic layer which connects the front P2 pole tip and back gap P2 pedestal to the yoke.
In published U.S. patent application 20030137771 by Hugo Santini a method of ion milling pole tips in a longitudinal write head is described. Photoresist is spun patterned to form a mask for ion milling to notch the bottom first pole tip layer adjacent first and second side edges of the top first pole tip layer.